Interpretive Summary: Many parts of the southeastern United States are best used as pasture land. Endophyte-infected tall fescue is widely grown in the southeastern and other parts of the United States, as well as in European countries, because of its persistence to grazing pressure. Ruminant animals grazing endophyte-infected tall fescue may experience hyperthermia, a reduction in feed intake, weight gain, as well as decreased pregnancy rates. The goal of the research was to evaluate reproductive performance of straightbred and crossbred hair sheep grazing tall fescue compared with bermudagrass overseeded with ryegrass. Pregnancy and lambing rate was similar between both forages for mature ewes, but may have decreased for yearling ewes grazing tall fescue. Observations are important to scientists, extenstion agents, and sheep and cattle producers as they suggest that the reproductive performance of sheep utilizing tall fescue in warm months is similar to that of forages lacking the endophyte.

Technical Abstract:
The objective of these studies was to evaluate reproductive performance of straightbred and crossbred hair sheep grazing tall fescue or bermudagrass forage. Body weight (BW) was measured in summers of 1998 through 2000 as well as fall 1999 on ewes grazing bermudagrass overseeded with ryegrass (BER) or tall fescue (FES) forage. Body condition score and serum concentrations of prolactin were determined in summer and fall 1999 and summer 2000. Breeds examined were St. Croix (SC), Romanov (ROM), and crossbred ewes. Pregnancy and lambing rate to summer and fall 1999 breeding and pregnancy rate to spring 2000 breeding was examined. Body weight and BCS reflected seasonal differences in forage availability between BER and FES, seasonal variations of toxins in FES forage, and breed differences. At all times measured, serum concentrations of prolactin were reduced in ewes grazing FES pastures (P<0.01) with the exception of summer 1999 where crossbred ewes grazing FES exhibited an increase compared with those grazing BER forage (forage x breed, P<0.03). Pregnancy and lambing rates were similar between forage treatments with the exception of a reduction in yearling crossbred ewes grazing FES in summer 1999 (P<0.05). Birth and weaning weights of lambs were similar between those suckling ewes grazing BER and FES forage. These experiments demonstrated that, in contrast to cattle, body condition of SC, ROM, and crossbred ewes can be maintained in an acceptable range with either BER or FES forage. Pregnancy rate may be reduced in yearling, but not older, ewes grazing FES forage. Birth weights and growth of lambs from mature ewes was similar between forage treatments.